Compound Interest Calculator
See how your savings grow over time
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Why does one savings account beat another when both advertise the same rate? Usually because of how often the interest compounds. The Compound Interest Calculator shows what that difference is worth over the years you actually plan to save for.
Short answer: The Compound Interest Calculator is a free EizTools tool that projects how savings grow over time. Give it a starting amount, a rate, a period and how often interest compounds, and it returns the figures with the working.
What is Compound Interest Calculator?
It projects growth on money that earns interest on its own interest. Describe your situation in the prompt box and the Compound Interest Calculator returns the final balance, the interest earned, and, if you ask for it, the year by year path between the two.
How Money Grows On Itself
Simple interest pays on your original amount only. Compound interest pays on the balance, which includes the interest already added, so the growth curves upwards instead of running in a straight line. The gap looks small in year one and large in year fifteen, which is the whole argument for starting early.
Useful for
- Comparing monthly, quarterly and yearly compounding on the same rate
- Seeing what a regular monthly contribution adds over a decade
- Understanding a rate rather than accepting the number on the advert
Honest limits
- It assumes a fixed rate, and real accounts change theirs
- Inflation, tax and fees are not in the sum unless you ask for them
- An AI model runs the arithmetic, so check anything you plan to act on
Precision And Detail Level
Two controls matter most here. Precision decides the rounding, and money questions usually want 2 Decimals rather than Auto. Detail Level, the slider at the bottom of the panel, decides how much the answer explains itself. Pushed high with Explain switched on, the result reads as a short walkthrough of where the growth comes from.
| Setting | Choices | Suggested start |
|---|---|---|
| Calculation Type | General, Math, Finance, Percentage, Conversion, Statistics, Date / Time, Custom | Finance |
| Output Style | Answer Only, Steps + Answer, Explanation, Detailed | Steps + Answer |
| Format | Plain, Table, Step-by-Step, Formula + Result | Table, which lays out the years cleanly |
How Does Compound Interest Calculator Work?
Someone saving for a deposit wants to compare two accounts at the same headline rate.
- Type the question: "8,000 saved at 4.2%, one account compounds monthly, one yearly, over 7 years, plus 150 a month."
- Choose a model in the selector before you run it.
- Choose Finance for the Calculation Type, Table for the Format, and hold precision at 2 Decimals.
- Turn on Show Formula and Explain, and push Detail Level above the middle.
- Generate, then read the yearly table rather than only the final figure.
- Download it as HTML if you want to keep the comparison somewhere.
The monthly compounding version comes out ahead, and the table shows where the gap opens up. Run it again with the monthly contribution removed and the difference between saving habits becomes obvious in a way a headline rate never shows.
Note Ask for the figure adjusted for inflation if the period is long. Money growing at 4% while prices rise at 3% is growing much more slowly than the headline suggests, and that line belongs in Custom Instructions.
Mistakes People Make
- Comparing accounts on rate alone, ignoring how often each one compounds
- Forgetting to include regular contributions, which usually matter more than the rate
- Projecting thirty years at a fixed rate and treating the result as a promise
- Leaving tax out entirely on savings that are not in a tax free wrapper
Nothing on EizTools requires a sign up or a payment, each tool is built for a single job, and the AI model family is chosen on the same screen. Savings maths tends to feed into bigger decisions, and the wider tool library covers the planning and writing work that usually follows a number like this one.
Frequently Asked Questions
Does the Compound Interest Calculator include monthly deposits?
Yes, if you mention them. Write the regular contribution into your prompt, such as "plus 150 a month", and it will be part of the projection rather than an afterthought.
Which compounding frequency should I compare?
Whatever your accounts actually use, usually monthly or yearly. Ask for both in one prompt and the difference on your own numbers becomes clear immediately.
Can it show the growth year by year?
Set Format to Table and ask for a yearly breakdown. That view is more useful than the final balance, because it shows when the compounding effect starts to matter.
Should I trust the projection?
Treat it as an estimate built on a fixed rate you supplied. Real rates move, and tax may apply. The arithmetic is checkable, and the tool shows its formula when you turn that on.
Compound growth is the one piece of personal finance maths worth understanding properly, because every other decision sits on top of it. Put your real numbers in, read the yearly table, and compare accounts on what they actually pay rather than what they advertise.
Sabir Bepari
Founder of EizTools and a passionate AI enthusiast dedicated to building practical, user-friendly AI tools that simplify everyday tasks.
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